Roller line or coating streak is a common problem for coatings, such as wall coatings, which makes the coating film aesthetically unacceptable. Roller lines are frequently encountered when the film's appearance is sensitive to differences in coating thicknesses that occur between the roper overlay areas, or when the film's appearance is sensitive to different curing mechanisms, e.g., one coating curing vs. wet to dry two coating curing wherein subsequent passes after initial application disturbs partially cured coating overlay areas. Coating formulations that minimize or eliminate unwanted lines, streaks, brush marks are typically desirable.
Fillers, fibers, cellulose or other components are used in many coating formulations to enhance the physical properties or chemical resistance of the cured coating film. For example, fiber reinforcing agents of various sizes and compositions are often added to coating formulations to improve physical performance and properties such as tensile strength and chemical resistance.
U.S. Pat. No. 6,214,450 discloses a high solids, e.g., about 65% to about 90% by volume solids, water-borne acrylic latex coating, useful as a roof coating, comprising an acrylic latex polymer, hollow particulates and very high pigment volume. Addition of a fiber to improve cohesion and flow characteristics of the coating is recommended. Cellulose fibers having an average length of 0.5 to 2 millimeters and an average fiber diameter of 10 to 20 microns are preferred because the cellulose hydroxyl groups are readily available to form hydrogen bonds with the latex polymer in a dispersion. The cellulose fibers also help to prevent the liquid surface coating from sagging on pitched substrates during drying. Short fibers made of polyethylene are also said to be useful.
Although addition of a filler or fiber can contribute to desirable physical properties of a coating film, it can also have adverse effects on properties such as viscosity or the film's appearance.
WO 2014/099702 discloses a composition comprising (a) at least one liquid resin; (b) a reinforcing modifier comprising flexible short fibers; and (c) a flow modifier comprising hybrid organic-inorganic particles bearing organic or hetero-organic groups that comprise substantially non-interacting groups; wherein the reinforcing modifier and the flow modifier are dispersed in the resin component. The flow modifier is added to the composition to improve the flowability of the resin, which is negatively affected by the presence of the short fibers.
The properties introduced to a coating by addition of a fiber or other filler depend on the composition of the fiber or other filler, and often on their size. For example, nanoparticles and micro fibers can impart a variety of properties to formulations, acting, for example, as rheology or viscosity modifiers, thixotropic agents, thickeners, reinforcing agents etc.
“Polymer, Fiber, and Filler Formulation Effects upon Ready-to-Use Grout”, The Waterborne Symposium: Proceedings of the Forty-First Annual International Waterborne, High-Solids, and Powder Coatings Symposium held in New Orleans, Louisiana, Feb. 24-28, 2014, p. 421, discusses improving various properties of grout formulations tensile strength, water resistance, stain repellence, cracking and shrinkage by addition of polymers, fibers and fillers. The fibers include fibrous polyethylene, nylon and cellulose.
US 2003/0119948 discloses a chip resistant automotive coating comprising a micro pulp slurry, which micro pulp comprises a fibrous organic material having a volume average length of from 0.01 to 100 micrometers and an average surface area of from 25 to 500 square meters per gram. A wide variety of fibers were said to be useful in the micro pulp, e.g., fibers made from aliphatic polyamides, polyesters, polyacrylonitriles, polyvinyl alcohols, polyolefins, polyvinyl chlorides, polyvinylidene chlorides, polyurethanes, polyfluorocarbons, phenolics, polybenzimidazoles, polyphenylenetriazoles, polyphenylene sulfides, polyoxadiazoles, polyimides, aromatic polyamides, cellulose, cotton or wool. Preferably the fibers were made from aromatic polyamides, polybenzoxadiazole, polyben-zimidazole, most preferably aromatic polyamides, e.g., (p-phenylene terephthalamide), poly(m-phenylene isophthalamide), or a mixture thereof.
US 2007/0149656 discloses a composition for producing a liner, e.g., a load-bearable coating to assist in protecting from rock bursts in a mine, comprising at least one water-borne, non-cellulosic precursor of a polyurethane and at least one wet pulp, for example, a composition comprising (a) at least one water-borne, non-cellulosic polymer dispersion, said polymer bearing groups that are reactive with isocyanate groups; (b) at least one hydrophilic prepolymer bearing isocyanate groups; and (c) at least one wet pulp comprising fibrous material selected from para-aramid fibers and mixtures thereof. “Wet pulp” means fibrous material that is capable of being fibrillated and that comprises at least about 20% by weight water, preferably at least about 40% and more preferably at least about 60 percent by weight water, based on the total weight of the wet pulp.
U.S. Pat. No. 8,734,940 discloses a diffusively reflective paint comprising a paint carrier, hollow and solid microspheres, and macroporous polymeric particles having an average diameter between about 1 micron and about 300 microns for use in reflectors in lighting fixtures. The macroporous polymeric particles are selected from the group consisting of flash spun plexifilamentary film-fibril materials, e.g., spun, high density polyethylene materials such as Tyvek®, microcellular foamed polyester sheets, biaxially-stretched polyester films, and combinations thereof. The paint carrier can further comprise a binder selected from acrylic binders, polyurethane binders, polyester binders and epoxy-based binders, and mixtures thereof. Acrylate binders, hybrid epoxy acrylate binders and a binder comprising a dispersion of a polyurethane resin were exemplified.
There remains a need for a safe, robust, readily mixed coating formulation, suitable for vertical surfaces such as walls, which is readily applied using common methods, and when applied, has an appearance that is less sensitive to thickness differences or other factors which may cause unwanted lines, streaks or other imperfections.